Method for enabling transmission of substantially equal amounts of energy

ABSTRACT

The invention relates to a method for enabling transmission of substantially equal amounts of energy from at least one light source (LS) comprising intensity variations in time to at least two light sensitive points (LSP), said transmission being controlled by means of at least one illumination arrangement ( 1 ), and said method comprising establishment of a correlation between said intensity variations and at least one feature of said illumination arrangement. The invention furthermore relates to an illumination arrangement ( 1 ) for controlling transmission of energy to at least two light sensitive points (LSP), wherein said controlling transmission enables transmission of substantially equal amounts of energy to each of said at least two light sensitive points (LSP).

FIELD OF THE INVENTION

The present invention relates to enablement of transmission ofsubstantially equal amounts of energy to at least two light sensitivepoints, in the context of illumination arrangements comprising lightsources with varying intensity.

BACKGROUND OF THE INVENTION

In several technical fields, illumination is either the main purpose oris used as a tool for obtaining desired results. Applications comprise,e.g., image and movie projection, photolithography, computer-to-plateapplications, serigraphy, other photographical applications such asproduction of printed circuit boards, etc., photolysis, rapidprototyping, rapid manufacturing, communication, and several others.

Numerous categories and types of light sources exist for illuminationpurposes, each manufactured with different purposes in view and oftenconstrained to neglect other purposes. Purposes of interest may be powerrating, luminous efficacy, stability of the luminous intensity,precision of the point of emission, color rendering, etc. For example,short arc lamps, i.e., high-pressure discharge lamps, are used in manyapplications because they may offer high power ratings, high luminousefficacy, excellent color rendering and a very small point of emission.Unfortunately, their construction, however, also causes displacement ofmaterial from the electrodes, causing their voltage ratings to changeduring use, their lifetime to be reduced, and the point of emission,i.e., the arc, to fluctuate. These problems are well known within theart and are addressed in several ways, some of which include the use ofalternating driving current and/or frequent current peaking. Often suchsolutions introduce new problems and in the example of short arc lamps,the current peaking causes the emitted luminous intensity to fluctuate.

Of the above mentioned illumination applications, several do acceptlight sources establishing light beams having fluctuating luminousintensity and/or fluctuating point of emission, either because they areintended for use in low-quality products, or because the fluctuationsmay be considered insignificant for a specific use. For example, for usein movie projectors, a slightly fluctuating luminous intensity may beacceptable as the light beam is used to illuminate the same areacontinuously, for which reason the human eye may not be able torecognize the changes and, furthermore, the projected images are changedat a fast pace. Such fluctuations may, however, not be acceptable forspecific uses of a high quality projector.

In fields as, e.g., photolithography and other techniques where theregion to be exposed is only illuminated little by little, fluctuationsof the luminous intensity may, however, be considered hazardous. This isbecause different regions of the exposed medium, e.g., a printing plate,are illuminated in turn, which makes it possible for one region to beilluminated with one level of intensity and the adjacent region to beilluminated with another. This may cause the result to look inconsistentand the probable periodicity of the intensity changes may even causestripes or other visible periodical patterns to occur.

One of several objects of the present invention is to establishcompensation means for facilitating the use of light sources withvarying luminous intensity, e.g., short arc lamps with additionalintensity at the supply peaking times, in applications where typicallyonly constant intensity lamps are used.

One of several objects of the present invention is to establish meansthat adapt to real-time changes in the level of periodically occurringadditional luminous intensity in a light beam and thus facilitatecompensation in order to utilize such a light beam in applications wheretypically only constant intensity light beams are used.

One of several objects of the present invention is to facilitate animproved uniform light transmission via a spatial light modulator, suchas, e.g., a DMD-modulator.

SUMMARY OF THE INVENTION

The invention relates to a method for enabling transmission ofsubstantially equal amounts of energy from at least one light source LScomprising intensity variations in time to at least two light sensitivepoints LSP, said transmission being controlled by means of at least oneillumination arrangement 1, and said method comprising establishment ofa correlation between said intensity variations and at least one featureof said illumination arrangement.

According to the present invention, disadvantages of using light sourceswith varying intensity, e.g., short arc lamps with peaking power supply,may be overcome, and in a preferred embodiment even in such a way thatthe peak intensities are utilized for optimum efficiency.

According to the present invention, energy is transmitted to lightsensitive points by accumulation of light intensity over time. Controlof the energy amount thus basically comprises control of the intensityand time of exposure.

The light originating from light sources according to the presentinvention may comprise intensities that vary in time, i.e., flickers,probably at a rate not perceptible by a human eye, and/or in space,i.e., non-uniform intensity distribution. It is an object of the presentinvention to particularly address the disadvantages of time wiseintensity variations.

In order to enable the use of peaking light sources and even utilizingthe intensity variations, a correlation between the variations and theenergy amount control means has to be present. Such correlation may,however, be established between the intensity variations and one or moreof several controllable features of the illumination arrangement, or thecorrelation may even be established by controlling the intensityvariations.

It is noted that the terms illumination arrangement and light modulatingarrangement in the following are used for substantially the same kind ofmeans.

When said intensity variations in time comprise substantially periodicintensity peaks, an advantageous embodiment of the present invention hasbeen obtained.

According to the present invention, the intensity variations of thelight source may comprise substantially periodic intensity peaks, as thelamp driver may intentionally cause such in order to prolong thelifetime of the lamp. As some lamp drivers may be controlled, it is, insome applications, possible to control the periodic intensity peaks,while still not possible to avoid them altogether.

When said at least one illumination arrangement 1 and said at least twolight sensitive points LSP are moved relative to each other, and wherebysaid at least one feature of said illumination arrangement comprisescharacteristics of said relative movement, an advantageous embodiment ofthe present invention has been obtained.

According to the present invention, the illumination arrangementpreferably travels relative to the light sensitive points in a directionparallel to a plane comprising the light sensitive points, i.e., a lightsensitive medium. Thus, some of several features that may be controlledin order to establish the correlation with the peak timing arecharacteristics of the movement, e.g., speed and direction, and also thewidth of the light modulation layout, i.e., the number of lightmodulators in each row.

When said establishment of a correlation comprises adapting saidcharacteristics of said relative movement into synchronism with saidintensity variations in time, an advantageous embodiment of the presentinvention has been obtained.

According to the present invention, the movement characteristics, e.g.,speed and direction, may be controlled in order to establish thecorrelation.

When said establishment of a correlation comprises adapting saidintensity variations in time into synchronism with said characteristicsof said relative movement, an advantageous embodiment of the presentinvention has been obtained.

According to the present invention, the intensity variations, e.g.,periodic intensity peaks, may be controlled in order to establish thecorrelation with the movement characteristics, e.g., speed anddirection.

When said synchronism between said intensity variations and saidcharacteristics of said relative movement comprise an integer number ofsaid periodic intensity peaks to occur during the illumination of eachof said at least two light sensitive points, an advantageous embodimentof the present invention has been obtained.

According to the present invention, the correlation should preferablycomprise an integer number of periodic intensity peaks occurring duringthe illumination of each light sensitive point. Thereby each lightsensitive point may receive a substantially equal amount of energy.

When said illumination arrangement 1 comprises at least one lightmodulation means 3, and whereby said at least one feature of saidillumination arrangement comprises characteristics of said lightmodulation means, an advantageous embodiment of the present inventionhas been obtained.

Characteristics of a light modulation means comprise, e.g., the currentlight modulation control information, the timing of the modulation, thespatial extent of the modulation, which light properties, e.g.,intensity, frequency, etc., are modulated, etc. According to the presentinvention, such characteristics may be controlled in order to establisha correlation with the intensity variations of the light source.

When said at least one light modulation means 3 comprises at least onespatial light modulator comprising a plurality of light modulators LM,an advantageous embodiment of the present invention has been obtained.

The spatial light modulator used in a preferred embodiment of thepresent invention is a DMD-chip. It comprises a plurality ofmicro-mirrors, i.e., light modulators LM. Specific characteristics of aspatial light modulator comprising a plurality of light modulatorscomprise, e.g., which light modulators to enable or disable, individualenabling times for each light modulator, etc. According to the presentinvention, such characteristics may be controlled in order to establisha correlation with the intensity variations of the light source.

When said controlling of said transmission by means of said at least oneillumination arrangement 1 comprises controlling said characteristics ofsaid at least one light modulation means 3 at least partly on the basisof at least one modulation mask MM defining light modulators to bedisabled, an advantageous embodiment of the present invention has beenobtained.

According to the present invention, control of characteristics of thelight modulating means is preferably achieved through the use ofmodulation masks. Such modulation masks may e.g., comprise informationof forced states of certain light modulators, and may be loaded into thelight modulating means by combining them with the utility image bitmap,thus establishing a composite bitmap to be loaded.

When said establishment of a correlation comprises adapting said atleast one modulation mask MM so that said characteristics of said atleast one light modulation means 3 is controlled in synchronism withsaid intensity variations in time, an advantageous embodiment of thepresent invention has been obtained.

According to the present invention, the modulation mask may be adaptedin order to correlate to the intensity variations. Such adaptations maybe predetermined or determined during exposure, and may comprise onelasting adaptation or several adaptations during exposure.

When said adaptation of said at least one modulation mask MM isperformed continuously, an advantageous embodiment of the presentinvention has been obtained.

According to the present invention, the modulation mask is adaptedcontinuously, in correlation with the intensity variations. Theadaptations may comprise choosing between predetermined modulation masksfrom a bank of modulation masks, determining modulation mask settings onthe fly, shifting a modulation mask to either side, etc. The adaptationmay also comprise adaptive adjustments according to variations in theperiodicity of the intensity variations.

When said adaptation of said at least one modulation mask MM compriseschoosing a predefined modulation mask from a bank of modulation masks,an advantageous embodiment of the present invention has been obtained.

When said at least one modulation mask MM further comprises controlinformation for avoiding non-uniform energy transmission due tointensity variations in space caused by said light modulation means oroptical features of said illumination arrangement 1, an advantageousembodiment of the present invention has been obtained.

According to the present invention, the modulation mask may, in additionto establishing a correlation of illumination arrangementcharacteristics with the time wise intensity variations, preferablycomprise information for handling spatial intensity variations.

When said establishment of a correlation comprises rearranging saidcontrol information in time, an advantageous embodiment of the presentinvention has been obtained.

According to the present invention, the spatial intensity variationshandling information may be rearranged in time, i.e., by switchingbetween different modulation masks comprising differently locatedcontrol information, through time.

When said establishment of a correlation comprises rearranging saidcontrol information in space, an advantageous embodiment of the presentinvention has been obtained.

According to the present invention, the spatial intensity variationshandling information may be rearranged in space, i.e., by shifting thecontrol information to either side, randomizing the control information,etc.

The present invention further relates to an illumination arrangement 1for controlling transmission of energy to at least two light sensitivepoints LSP, wherein said controlling transmission enables transmissionof substantially equal amounts of energy to each of said at least twolight sensitive points LSP, an advantageous embodiment of the presentinvention has been obtained.

According to the present invention, illumination arrangements may beenabled to transmit substantially equal amounts of energy to lightsensitive points, thereby overcoming disadvantages of intensity varyinglight sources.

According to the present invention, an illumination arrangement, alsoreferred to as a light modulating arrangement, preferably comprisesmeans for establishing a light beam, modulating the light beam into aplurality of individually controlled light beams, and directing thelight beams towards a light sensitive medium.

When said illumination arrangement comprises at least one light sourceLS, an advantageous embodiment of the present invention has beenobtained.

When said at least one light source LS submits light comprisingsubstantially periodic intensity variations, an advantageous embodimentof the present invention has been obtained.

According to the present invention, the driver of the light source mayintentionally establish periodic intensity variations. By means of thepresent invention, the disadvantages of this often necessary evil mayeven be turned into more efficient illumination of light sensitivemedia.

When said illumination arrangement comprises at least one lightmodulation means 3, an advantageous embodiment of the present inventionhas been obtained.

When said at least one light modulation means 3 comprises at least onespatial light modulation means, an advantageous embodiment of thepresent invention has been obtained.

When said at least one spatial light modulation means 3 comprises aDMD-chip, an advantageous embodiment of the present invention has beenobtained.

When said at least one spatial light modulation means 3 comprises amicro-mechanical shutter array, an advantageous embodiment of thepresent invention has been obtained.

When said illumination arrangement is moved relative to said at leasttwo light sensitive points, an advantageous embodiment of the presentinvention has been obtained.

According to the present invention, the illumination arrangementpreferably travels relative to the light sensitive points in a directionparallel to a plane comprising the light sensitive points, i.e., a lightsensitive medium.

When said transmission of substantially equal amounts of energy to eachof said at least two light sensitive points LSP is at least partlyenabled by means of controlling said relative movement between saidillumination arrangement and said at least two light sensitive points,an advantageous embodiment of the present invention has been obtained.

According to the present invention, equal amounts of energy may beensured by characteristics of the movement, e.g., speed and direction,and also the width of the light modulation layout, i.e., the number oflight modulators in each row.

When said controlling of said relative movement comprises synchronizingsaid relative movement with said period intensity variations, anadvantageous embodiment of the present invention has been obtained.

According to the invention, the controlling of the movement, e.g., speedand direction, should preferably cause the movement to be synchronizedwith the intensity variations.

When said transmission of substantially equal amounts of energy to eachof said at least two light sensitive points LSP is at least partlyenabled by means of controlling said light modulation means 3, anadvantageous embodiment of the present invention has been obtained.

According to the present invention, controlling the light modulationmeans may ensure the substantially equal amounts of energy. Featuresthat may be controlled comprise, e.g., which light modulators to enableor disable and the enabling times of each light modulator. Thecontrolling may furthermore comprise features such as intensityattenuation, wavelength filters, etc.

When said controlling said light modulation means 3 comprises applyingat least one modulation mask MM, an advantageous embodiment of thepresent invention has been obtained.

According to the present invention, modulation masks are preferably usedfor controlling the light modulation means. A modulation mask may, e.g.,comprise control information on each light modulator of the lightmodulation means, such as forced disabling or enabling of each lightmodulator. The modulation mask may preferably be loaded into the lightmodulation means by combining it with the utility bitmap to be exposed,and then loading the composite bitmap.

When said at least one modulation mask MM is established on the basis ofcharacteristics of said periodic intensity variations, an advantageousembodiment of the present invention has been obtained.

According to the present invention, properties of a modulation mask ispreferably determined on the basis of characteristics of the intensityvariations, e.g., frequency, durations, etc. Thereby a correlationbetween the intensity variations and the control of the light modulatingmeans may be established, allowing transmission of substantially equalamounts of energy.

When said at least one modulation mask MM further comprises controlinformation for handling further disadvantages of said illuminationarrangement, an advantageous embodiment of the present invention hasbeen obtained.

According to the present invention, further disadvantages of theillumination arrangement may comprise limitations in the optical design,the light modulation means, among others, typically causing the lightintensity distribution over the light modulation layout to benon-uniform, and furthermore typically causing non-linear orasymmetrical distortion in the edges and corners of the light modulationlayout.

According to the present invention, the modulation masks may beestablished in such a way that both the time wise intensity variationsas well as the further disadvantages of the illumination arrangement maybe addressed.

When said controlling of said light modulation means 3 comprisesrearranging said control information for handling further disadvantages,an advantageous embodiment of the present invention has been obtained.

According to the present invention, the controlling of the lightmodulation means comprises rearranging of the information for handlingthe further disadvantages. Thereby this control information ispreserved, however in amended form, in order to address both problems.

When the illumination arrangement comprises means for carrying out theabove-described method, an advantageous embodiment of the presentinvention has been obtained.

THE DRAWINGS

The invention will in the following be described with reference to thedrawings where:

FIG. 1A illustrates an embodiment of a light modulating arrangement,

FIG. 1B illustrates a preferred movement pattern of the arrangement,

FIG. 2A illustrates an example of a light modulation layout,

FIG. 2B illustrates movement of the light modulation layout relative toa medium, FIG. 3A illustrates timing diagrams of the light source,

FIG. 3B illustrates further timing diagrams of the light source,

FIG. 4 illustrates disadvantages of known techniques,

FIG. 5 illustrates the effect of an embodiment of the present invention,

FIG. 6 illustrates measuring of intensity distribution over a lightmodulation layout,

FIGS. 7A-7C illustrate examples of modulation masks,

FIG. 8A illustrates a further example of a modulation mask,

FIG. 8B illustrates moving the modulation mask over a medium,

FIG. 8C illustrates the result of illumination on the basis of themodulation mask, FIG. 9A illustrates a bank of modulation masks,

FIG. 9B illustrates circulating through the mask bank during exposure,and

FIG. 9C illustrates a result of illumination on the basis of amodulation mask bank.

DETAILED DESCRIPTION

FIGS. 1A and 1B illustrate a preferred application of the presentinvention. FIG. 1A illustrates a light modulating arrangement 1 used forphotolithography purposes, i.e., typically for exposing printing plates.A first part 2 of the arrangement 1 produces a focused and uniform beamof light. It comprises a light source LS, a lamp driver LD, a blower 25and a fan 26, a protection glass and filter 21, a shutter 22, alight-integrating rod 23 and beam shaping optics 24.

The type of light source LS depends, among other things, on the type ofplate to be exposed. Possible types comprise conventional short arcbulbs, laser sources, diode arrays and more. A preferred conventionallamp may have a power consumption of 270 W but the present invention isnot in any way limited to this value or to the mentioned types of lamps.Alternatives such as 250 W and 350 W may, e.g., be considered.

The light from the light source LS is transmitted through a filter(e.g., IR or UV-filter depending on the application) 21 functioning asan interference filter and through a shutter mechanism 22 making itpossible to turn off the light beam without turning off the lamp. Thisis important, as most lamp types need some time after start before theyare stabilized. A blower 25 and a fan 26 ensure the cooling of the lampLS.

Subsequently, the light beam is transmitted through a light-integratingrod 23. Thereby, the light is mixed, making the light throughout thebeam uniform with regards to intensity. This ensures that the light inthe periphery of the beam has substantially the same intensity as thelight in the center of the beam. After the light leaves thelight-integrating rod 23, it is focused by beam shaping optics 24.

The next part of the arrangement 1 modulates the light beam to reflectelectronically stored image data. It comprises a light-modulating means3 and means 35 for directing the unmodulated light beam towards thelight-modulating means 3 without disturbing its modulated light beamoutput.

Suitable light-modulating means 3 comprises micro-mirror spatial lightmodulators, e.g., DMD modulators or GLV modulators, transmissive shutterspatial light modulators, including LCD and micro-mechanical shuttersand more. For the preferred embodiment of FIG. 1A, a DMDlight-modulating chip 31 is mounted on a PCB 32 with a cooling plate 33and a temperature sensor 34.

The light directing means 35 depends on the type of light-modulatingmeans 3 used. For transmissive light modulating means, the unmodulatedlight beam is directed towards one side of the light modulating means,and the modulated light beam is emitted from the other side. In such anarrangement, the light directing means 35 may be excluded.

For DMD modulators, the unmodulated light beam is directed towards thesame point as where the modulated light beam is emitted. Thisnecessitates the use of light directing means 35. In the preferredembodiment of FIG. 1A, a TIR-prism is used for light directing means.TIR is an abbreviation meaning ‘Total Internal Reflection’.

A TIR-prism comprises a surface 36 which will act as a mirror to lightcoming from one direction (from the left for this specific embodiment)and will let light coming from another direction (from the top for thisspecific embodiment) straight through.

The last part of the arrangement 1 focuses the multiple modulated lightbeams emitted from the light modulating means 31 through the lightdirecting means 35 on an illumination surface 5, e.g., a printing plate.It comprises a set of lenses/a macro lens 41 located within a housing 4.

FIG. 1B illustrates how the light modulating arrangement 1 of FIG. 1Amay be used for exposing a printing plate or other kind of lightsensitive media 5. Due to clearance, only the light modulating means 3and lens housing 4 of the arrangement 1 is shown in FIG. 1B.Furthermore, the figure shows a light modulation layout LML establishedby the light modulating arrangement on the surface of the lightsensitive media 5. In order to expose the whole light sensitive media 5,the light modulation layout LML, and thereby the light modulatingarrangement 1, and the light sensitive media 5 must be moved withrespect to each other in such a way that the light modulation layouteventually has covered the part of the plate that needs to be exposed.This is preferably done by facilitating a scanning movement, e.g., asindicated by the dashed lines, of the light modulation arrangement withrespect to the plate, e.g., by letting the light modulation arrangementscan the width of the plate, then move the plate one step forward alongits length, then perform a second scan in the opposite direction asbefore, and so forth.

It is noted that the present invention has several further uses thandescribed above with reference to FIGS. 1A and 1B. It may, furthermore,advantageously be used, e.g., for exposing printed circuit boards inconnection with the manufacture of such boards, rapid prototyping, i.e.,manufacture of three-dimensional models by a process well-known as rapidprototyping, exposing offset plates and films and, e.g., in serigraphyapplications, in photo finishing processes, in biomedical applications,e.g., for research regarding DNA profiles, in projection applicationsand signs, in digital cinema applications, etc., and in any otherapplication or process comprising light sources and where accuratecontrol of the energy transmitted to a light sensitive media isimportant.

The light source LS is preferably a short arc lamp, i.e., ahigh-pressure discharge lamp, and will in the following be treated assuch even though it, within the scope of the present invention, may beany light-emitting device comprising, e.g., incandescent lamps of anytype, fluorescent lamps, light emitting diodes (LEDs), laser emitters,etc. The short arc lamp may be of any type, e.g., metal halide lamps,mercury vapor lamps or sodium vapor lamps, etc. and is preferably analternating current (AC) lamp but may as well within the scope of theinvention be a direct current (DC) lamp or a lamp with moresophisticated power requirements. The light source is preferablyprovided with one or more reflectors or other light direction means inorder to establish a light beam with as high luminous intensity aspossible.

The lamp driver LD may be any kind of power supply suited to drive theparticular light source. In the case of a short arc lamp as lightsource, the lamp driver LD preferably establishes an alternating current(AC) with peaking in order to extend the lifetime of the lamp andstabilize the position of the arc. Alternatively for a suitable shortarc lamp, the lamp driver LD may establish a direct current (DC) withpeaking or otherwise varying current or voltage, e.g., saw-tooth shaped.The lamp driver LD is preferably a current source but may as well withinthe scope of the invention be a voltage source.

FIG. 2A illustrates an exemplary light modulation layout LML. Itcomprises a two-dimensional array of light modulation points LMP. Thearray comprises a number of rows RO-R1023 and a number of columnsC0-C767. The exact number of rows and columns may be anything and is forthis specific example chosen to be 1024 rows and 768 columns,corresponding to XGA resolution. Thus, the light modulation layout LMLof this example comprises 786.432 light modulation points LMP. Anotherpreferred example is to have 1280 rows and 1024 columns, correspondingto SXGA resolution, or 1280 rows and 720 columns, corresponding to an HDresolution.

It should be noted that the use of the terms rows and columns in thispatent application may differ from the use in other application. e.g.,concerning displays or monitors. Particularly, the use of the terms isswapped in some applications.

Each light modulation point LMP corresponds to a light modulator LM,e.g., a micro-mirror, of the light modulating means 3, e.g., a DMD chip.The content, e.g., light or not light, of each light modulation pointLMP directly corresponds to the setting of the corresponding lightmodulator LM, and as each light modulator LM may be individuallycontrolled by the light modulating means 3, each light modulating pointLMP may correspondingly be individually established by the lightmodulation means 3. In a preferred embodiment of the light modulatingarrangement, only the existence of light in each light modulation pointLMP is controlled by the light modulating means 3 but it is within thescope of the invention to also let the light modulating means controlother parameters of the light as e.g., the intensity or the wavelength(color) etc.

In a preferred embodiment of the light modulating arrangement of FIG.1A, the light modulating means 3 comprises a DMD light-modulating chip31. The surface of the chip, which is exposed to the unmodulated lightbeam, is covered by hundreds of thousands or millions of small mirrors,arranged in a two-dimensional array. Typically, a chip comprises1024×768 mirrors or 1280×1024 mirrors. Each mirror constitutes a lightmodulator LM and is able to direct the incoming light in two directions.A first direction towards the optics 41 and the light sensitive media 5,and a second direction towards some light absorbing material. Thus, themodulated light beam actually consists of many sub beams, each beingreflected from one of the small mirrors. By controlling the direction ofeach mirror, i.e., light modulator LM, it is possible to control whichof the light modulation points LMP of the light modulation layout LMLthat receives light at a specific time.

Several other embodiments of light modulation arrangements, lightmodulation means, etc., e.g., the use of micro-mechanical shutters, morethan one light modulation means, different movement patterns, etc.,within the scope of the present invention, are disclosed in the PCTpatent application published as WO 2004/021269, hereby incorporated byreference.

In the following description, when mentioning a light modulator LM beingturned on or off, it indicates whether or not it illuminates itscorresponding light modulation point LMP. Furthermore, the presentinvention is in the following described in the context of a lightmodulating arrangement according to FIG. 1A, comprising a DMD spatiallight modulator, establishing a light modulation layout LML according toFIG. 2A and exercising a movement pattern according to FIG. 1B. It is,however, noted that any light modulating arrangement comprising anylight modulating means, establishing any kind of light modulation layoutand exercising any movement pattern is within the scope of the presentinvention.

FIG. 2B shows how the movement pattern of FIG. 1B causes each point LSPon the light sensitive media to be exposed to the possible light ofseveral light modulators LM. It is noted that the reference to points onthe light sensitive media does not necessarily refer to physicallydefined points on the media but rather to points logically defined bythe light modulation layout LML. Hence, the light sensitive media mayactually have point resolutions of significantly smaller size, e.g.,molecule size, than the points relevant to the present description.

Due to reasons of clarity, the light modulation layout LML is shown withmuch fewer light modulation points LMP as in a preferred embodiment. Asthe light modulating arrangement, and thereby the light modulationlayout LML, moves over the light sensitive media 5 in the directionindicated by the arrow, each point on the light sensitive media possiblyreceives light from several light modulators but always from lightmodulators located in the same row. For example, the specific lightsensitive point LSP on the light sensitive media receives light onlyfrom the light modulators located in the row R2, which are on at thetime they are over that point LSP. When the light modulation layout hasmoved over the specific point LSP, that point has altogether receivedenergy corresponding to a time-based accumulation of the light intensityfrom each light modulator in the row R2 that is turned on. Each pointmay, however, receive light from more than one row of light modulatorsLM if an overlapping movement pattern is used, or if the lightmodulating arrangement comprises more than one light modulating means.

In an alternative embodiment within the scope of the present invention,the light modulation arrangement 1, and, thus, the light modulationlayout LML, may move stepwise over the light sensitive media 5, eachstep being preferably the width of the light modulation layout LML.

Thereby, each light sensitive point LSP is only illuminated once andonly by one light modulator LM. The energy accumulation does, thus, inthis alternative embodiment not depend on the number of light modulatorsilluminating it by a scanning movement but rather of the time span theone light modulator is positioned (and turned on) over a specific lightsensitive point.

It is noted that combinations of the scanning and step movement patternsand any other moving and illumination patterns are within the scope ofthe present invention.

Typically, the light sensitive medium 5, e.g., a printing plate, is bymeans of, e.g., a DMD-based light modulation arrangement 1 exposed to adesired image by looping through an algorithm comprising the steps of:(1) on the basis of digitally stored information about the full orpartial image to expose, establishing a bitmap comprising settings foreach of the light modulators LM for the current relative positionbetween the light modulating arrangement 1 and the light sensitivemedium 5, (2) loading the established bitmap into the DMD-chip internalmemory, (3) instructing the DMD-chip to engage the light modulators LMaccording to the loaded data, (4) after a certain time determined on thebasis of, e.g., the scanning speed, peak timing, etc., instructing theDMD-chip to disengage the light modulators LM.

It is noted that the above example algorithm is merely provided in orderto ease the following description, and that any algorithm is within thescope of the present invention. It is, furthermore, noted that the abovealgorithm is designed for use with DMD-based light modulatingarrangements and, thus, may not work with other light modulating meanswithout modifications. Such modifications may, however, typically beretrieved or determined fairly easily from the manuals corresponding tothe specific light modulation means.

Also, in order to clarify the following description of the invention,the above-mentioned desired image is in all following examples chosen tobe an image that will in itself cause all light modulators to be turnedon, i.e., an all-white or all-black image depending on the media type,either negative or positive. By choosing such an image for the examples,the characteristics of the light modulation arrangement, the DMD, thespecific embodiments, etc., stand out more clearly than when blurred byan example image. Thus, the following illustrations, values, etc., mayonly be true for this specific test image whereas the principles aretrue for any applied image.

FIGS. 3A and 3B illustrate problems that may follow using a lamp thatrequires AC power with peaking as described above. FIG. 3A comprisestiming diagrams of the voltage V_(LS) and current I_(LS) that in oneembodiment of the invention is applied to the light source LS. In theshown example, the lamp driver establishes an alternating current withpeaking. The lamp driver outputs an alternating current I_(LS) that, inaddition to a positive and negative current floor CF value, comprisescurrent peaks CP prior to each direction shift. The voltage V_(LS) overthe lamp alternates in the shown example between a positive and anegative voltage floor VF value, and comprises voltage peaks VP incorrespondence to the current peaks. Both the voltage and the currentwaveforms are preferably square waves to ensure only very short periodsof voltages in the region of the ground potential, usually 0V. Becauseof the current peaks CP, the electrical power consumed by the lightsource will not be constant as the power may be evaluated as the productof the RMS current and the RMS voltage.

Examples of actual values in the case of a short arc lamp driven by ACwith peaking, may comprise a voltage floor VF of, e.g., 77-140 volts, acurrent floor CF of, e.g., 1.7-3.3 amperes, current peaks CP of, e.g.,150-200% of the current floor CF value, a V_(SAL) period time of e.g.,3-10 ms, and current peaks CP having a duration of, e.g., 200-600 μs. Itis noted that the present invention is in no way restricted to thevalues, waveforms, etc., mentioned above. An often-used alternativetiming scheme for short arc lamps is a direct current scheme withsaw-tooth shaped current.

It is well known within the art that applying current peaks to a shortarc lamp significantly improves its usability within precisionapplications as the position of the arc becomes less fluctuating and,thereby, also the point of light emission.

FIG. 3A further illustrates the resulting luminous intensity LI_(LB) ofthe light beam established by the light source LS. As the luminousintensity is derived from the consumed electrical power, it comprises anintensity floor IF being proportional with the multiple of the voltagefloor VF and the current floor CF and intensity peaks IP inherited fromthe current peaks CP having a value proportional with the multiple ofthe voltage floor VF and the current peak CP. The intensity peaks IPare, thus, a trade off for improved precision but are, nevertheless,unacceptable in many applications where a substantially constantluminous intensity is necessary.

The diagram of LI_(LB) clearly illustrates one problem that the presentinvention may address. As the luminous intensity of the light beam LBcomprises intensity peaks IP, any area exposed to the light beam LB willexperience inconstant illumination. While this may be acceptable forsome applications, e.g., projectors where the light beam is used toilluminate the same area continuously, it is not acceptable forapplications within several areas as, e.g., photolithography and othertechniques where the region to be exposed is only illuminated little bylittle. This is because the human eye is better to judge the relativeintensities of, e.g., two dots established individually and presentedside by side than intensity changes of one dot. Additionally, theperiodicity of the intensity peaks may, in unfortunate incidents, causestripes or other visible periodical patterns to occur.

Whereas FIG. 3A illustrates a continuous problem that may follow fromusing peaked AC lamps, FIG. 3B illustrates a further problem that isderived from the above, but only becomes significant over a considerabletime. The timing diagram of FIG. 3B corresponds in many ways to thetiming diagram of FIG. 3A, yet the time axes, however, have beenextended far beyond those of FIG. 3A. The far longer time period isindicated by the breaks on each time axis. Each break corresponds toseveral hours, e.g., 200 hours.

The first diagram illustrates the voltage V_(LS) over the light sourceLS. It is a square waveform as in FIG. 3A but the voltage floor VFincreases with time of use. This is caused by the electrode gap of theshort arc lamp slowly growing wider during use because of displacementof electrode material. A wider gap necessitates a higher voltage inorder for the electrons to jump the gap and, thus, establishes thelight-emitting arc.

As the power consumed by the light source should be substantially fixedin order for the luminous intensity of the light beam to be constant,the increase in electrical resistance represented by the electrode gapcauses an increase in voltage and a decrease in current, as the power isdetermined by the multiple of the voltage and the current. The seconddiagram of FIG. 3B shows three snapshots of the light source currentI_(LS) at different times during use. It is seen that the current floorCF decreases as the voltage floor increases. The current peaks CP are,however, maintained at a constant value as the lamp driver LD ratherthan the power dissipation of the light source LS determines thatspecific value.

The third diagram of FIG. 3B illustrates the luminous intensity of thelight beam LI_(LB) established by the light source on the basis of thevoltage and current schemes of FIG. 3B. As the luminous intensity isproportional with the electrical power, the intensity is maintained at aconstant level indicated by the intensity floor IF, whereas theintensity of the intensity peaks IP increases due to its correspondencewith the multiplication of an increasing voltage with a constantcurrent.

FIG. 4 illustrates how the intensity peaks IP comprised by the lightbeam may influence the energy accumulated in each light sensitive pointLSP of the media 5. It comprises, at the top, a copy of the last diagramof FIG. 3B, i.e., a timing diagram of the intensity of the light beamestablished by the light source. Underneath that, i.e., sharing the timeaxis with the light intensity diagram, is a diagram of the energy Eaccumulated in three subsequent light sensitive points LSP1, LSP2, LSP3.The diagram, thus, illustrates the result of moving the light modulatingarrangement 1 over the three light sensitive points LSP1, LSP2, LSP3.Underneath the time axis, the time spans are indicated in which eachpoint is exposed, i.e., the time it takes the light modulation layoutLML to pass over the points. As the curves show the accumulated energy,the slope of the curves are steeper during intensity peaks of the lightbeam. As seen from the diagram, three intensity peaks occur during theexposure of the first light sensitive point LSP1, only two peaks occurduring the exposure of the next light sensitive point LSP2, and abouttwo and a half peaks occur during the exposure of the third lightsensitive point LSP3. Thereby, the energy accumulated in the first pointLSP1 is higher than the energy accumulated in the third point LSP3,which again is higher than the energy accumulated in the second pointLSP2.

For several applications, e.g., photolithography, the energydifferences, however small they may be, may easily cause unacceptableresults, e.g., periodic stripes on a printing plate, etc. The problem isclosely connected to the relation between the frequency of the intensitypeaks and the scanning speed of the light modulation layout. If, e.g.,several hundreds of peaks occur within the exposure of each lightsensitive point LSP, one or two more or less may not cause unacceptableenergy differences. But typically the desirable peak frequency and thedesirable scanning speed is related in such a way that the problem issignificant and unacceptable.

In an embodiment of the present invention, synchronizing the scanningspeed with the peak frequency solves the problem. This solution is shownin FIG. 5. The scanning speed is adjusted in such a way that theexposure time for one light sensitive pixel corresponds to exactly aninteger number of peaks, e.g., three peaks as in the example of FIG. 5.Thereby, the accumulated energy in each light sensitive point LSP1, LSP2and LSP3 is the same as shown in FIG. 5.

The synchronization between the scanning speed and the peaks may beestablished by measuring or otherwise determining the exact peakfrequency and adjusting the scanning speed according to that, oroppositely by measuring or otherwise determining the scanning speed andadjusting the peak frequency according to that. In another embodiment ofthe invention, the peak frequency and scanning speed are both variablesand may be adjusted during exposure as long as the synchronizationbetween them are maintained. Alternatively, or in combination with theabove, the synchronization may be established by adjusting the number ofcolumns of the light modulation layout, i.e., its width. As lightmodulating means, e.g., DMD-chips, are typically only manufactured in afew different dimensions, adjusting the width of the light modulationlayout may in practice be done by choosing a modulation means, e.g., aDMD-chip, which is too wide and then just use a part of its width.

More advanced light modulating arrangements or other means forilluminating more than one point at a time comprise means forcompensating intensity variations in the cross section of the light beamor anything else that may distort the intensity uniformity over thelight modulation layout. Actually, due to limitations in the opticaldesign, the light modulating means, etc., the light intensitydistribution over the light modulation layout is typically not uniformand the distortion is typically not linear or symmetrical either.Usually the light intensity is highest in or somewhere near the middleof the light modulation layout and it is lowest and most distorted inthe corners. In order to compensate for that non-uniformity, filters ormasks are introduced.

A brief description of one method to determine the actual intensitydistribution is given with reference to FIG. 6. It comprises an examplelight modulation layout LML that is moved by a scanning movement over ameasuring line 61. The measuring line may, e.g., comprise a column ofintensity or energy meters, one for each row of the light modulationlayout. The results from the measuring line 61 may be used to establisha diagram as shown on the right in FIG. 6. It comprises the accumulatedenergy E for each row. Thereby, it is possible to determine the leastintense row and use its accumulated energy potential as a commondenominator for all rows indicated by the dashed line 62. If no rowsubmits more energy to an individual light sensitive point than thedetermined common denominator 62, or an even lower level for safety orother reasons, a uniform intensity distribution may be achieved.

In order to force all rows to only submit the energy corresponding tothe least intense row, or even less, masks are established. FIGS. 7A to7C illustrate a few of several possible modulation masks MM for use witha light modulating arrangement for counteracting the non-uniformintensity distribution. The arrows indicate the intended travelingdirection, i.e., the direction along the rows of the light modulationlayout. A mask indicates a number of light modulators, e.g.,micro-mirrors, which should be turned off in order to not exceed thedetermined common denominator 62, or a lower safe level. In FIGS. 7A to7C, the black areas denote light modulators that should not be used.Clearly the masks in these figures are intended to compensate for adistribution pattern where the intensity is highest in the center anddecreases towards the edges, also illustrated in FIG. 6, by allowingmore light modulators to be applied in the top and bottom rows than inthe middle rows. The FIGS. 7A and 7B illustrate fairly simple masks thatdo not take into account the possible distortion along the rows of thelight modulation layout, whereas FIG. 7C illustrates a more advancedmask pattern where the blocked light modulators are distributedheterogeneously or pseudo-randomly or randomly along the rows. This lastembodiment also compensates for the distortion along the rows as eachrow will use light modulators from the edge-areas as well as the centerarea for illuminating each light sensitive point.

Regarding the algorithm described above, the use of masks causes anadditional step to be inserted, such that typically the light sensitivemedium 5, e.g., a printing plate, is by means of, e.g., a DMD-basedlight modulation arrangement 1, exposed to a desired image by loopingthrough an algorithm comprising the steps of: (1A) on the basis ofdigitally stored information about the full or partial image to expose,establishing a bitmap comprising settings for each of the lightmodulators LM for the current relative position between the lightmodulating arrangement 1 and the light sensitive medium 5, (1B)establishing a composite bitmap by combining the established bitmap witha modulation mask MM by means of a bitwise AND-operations, (2) loadingthe established composite bitmap into the DMD-chip internal memory, (3)instructing the DMD-chip to engage the light modulators LM according tothe loaded data, (4) after a certain time determined on the basis of,e.g., the scanning speed, peak timing, etc., instructing the DMD-chip todisengage the light modulators LM.

It is yet again noted that the above example algorithm is merelyprovided in order to ease the description, and that any algorithm iswithin the scope of the present invention. It is, furthermore, notedthat the above algorithm is designed for use with DMD-based lightmodulating arrangements and, thus, may not work with other lightmodulating means without modifications. Such modifications may, however,typically be retrieved or determined fairly easily from the manualscorresponding to the specific light modulation means.

A more thorough description of the use of masks, how to determine theintensity distribution, parameters to take into account when designingthe masks, as well as several different embodiments attacking the issue,are disclosed in the PCT patent application published as WO 2004/021269,hereby incorporated by reference.

Turning back to the problem of intensity variations due to light beamintensity peaks, the embodiment described above with reference to FIG. 5may not work when masks as described above are used for compensating fornon-uniform intensity distribution over the light modulation layout.This is because this embodiment implies the use of all light modulators,e.g., micro-mirrors, in each row, or at least the same number ofmodulators in each row. When a different number of light modulators, ordifferently positioned light modulators, are used in each row, it islikely that for some rows the unused light modulators pass over acertain light sensitive point at the time of a peak, whereas the unusedmodulators in other rows pass over a corresponding light sensitive pointat the time of an intensity floor.

The problem is illustrated in FIGS. 8A to 8C. In FIG. 8A is shown anexample of a modulation mask MM due to clarity again only comprising afraction of the rows and columns typically comprised. As regards FIGS.7A-7C, the black pixels are blocked, i.e., forcing the correspondinglight modulators LM to stay turned off. FIG. 8B illustrates the movementof the light modulation layout over the light sensitive medium 5, e.g.,a printing plate. It comprises a fraction of a light sensitive medium 5showing four light sensitive points LSP1, LSP2, LSP3 and LSP4 positionedadjacent to each other in the same row on the plate. In the right sideof FIG. 8B is shown an intensity peak timing diagram, having a verticaltime axis and a horizontal intensity axis. The vertical time axiscomprises marks showing the illumination time for each light sensitivepoint and the pauses between the light modulator engagements.

Furthermore, FIG. 8B illustrates the traveling of one modulation maskrow MMR over the four light sensitive points by illustrating theposition of the modulation mask row at different times corresponding tothe vertical time axis. The modulation mask row MMR is in this examplethe fourth row of the modulation mask MM of FIG. 8A. At times where anintensity peak occurs, a “p” is written on the modulation mask row inorder to ease reading of the diagram.

In the present illustration, the scanning speed is synchronized with thepeak frequency as in the embodiment of FIG. 5. As the mask row movesover the light sensitive points, these are illuminated by standardintensity, illuminated by peak intensity, or blocked. The actualillumination may, thus, be determined from combining the mask, thescanning speed and the peak timing. Each of the columns 81, 82, 83, 84below the light sensitive points, thus, comprises the individualexposures of each point at different times. It may, e.g., be seen thatthe first light sensitive point LSP1 has been exposed to standardintensity three times, to peak intensity three times, and to no lightthree times. Analogously, the second light sensitive point has beenexposed to standard intensity four times, to peak intensity twicebecause of the coincidence between a peak and a blocking, and to nolight three times. The third light sensitive point has been exposed tostandard intensity five times, to peak intensity only once because ofthe coincidences between the peaks and blockings, and to no light threetimes.

FIG. 8C comprises a diagram showing the energy accumulation takingplace. It again comprises an intensity peak timing diagram correspondingto a horizontal time axis. Below the time axis, the columns 81, 82, 83and 84 of FIG. 8B are shown but they have been rotated 90 degreescorresponding to the time axis. It is, thus, possible to see from FIG.8C what is experienced by each light sensitive point LSP1, LSP2, LSP3and LSP4 and at which times. Below that, an energy diagram shows theaccumulation of energy for each light sensitive point as determined fromthe experience columns 81, 82, 83, 84. Clearly, the different pointsattain different energy levels because of the different number of peaksexperienced by each point, even though the scanning speed is actuallysynchronized with the peak timing in the present example.

In order to overcome the problem of the modulation mask coinciding withthe intensity peaks for some light sensitive points, the mask is in apreferred embodiment of the invention adapted so that it is locked tothe peak timing rather than to the scanning movement, thereby ensuringthat if one light sensitive point receives an intensity peak due to themask, all light sensitive points will receive that peak, and if a peakis blocked regarding one light sensitive point due to the mask, no lightsensitive points receive that peak. FIGS. 9A to 9C are provided toillustrate this.

Instead of moving the mask with the light modulation layout LML, themask is now fixed to the time, i.e., to the peak timing, and, thus,actually also to the light sensitive media when taking the scanningspeed into account. In order to ensure that an intensity peak is eitherabsorbed by all or none of the light sensitive points within a row, itis necessary to treat all light modulators within that row equally atthe peak times, i.e., either turned on or off. As turning all lightmodulators off all the time obviously causes no exposure to happen, andturning all light modulators on all the time obviously causes the use ofmasks against non-uniform distribution impossible, a runtime adaptationof the mask is a possibility. This may comprise either establishing abank of different masks to use at different times or establishing analgorithm from which it is possible to always establish a mask thatcorresponds to the current time.

Several possible mask adaptation patterns may be used in order to obtainthe row-wise common acceptance or rejection of peaks. FIG. 9Aillustrates one such possible scheme. As the primary objective of usinga modulation mask as, e.g., the example shown in FIG. 8A, is to ensureuniform energy accumulation for all rows, a mask row comprising, e.g.,three blocked light modulators out of nine may as well be implemented byblocking all of that row's light modulators during three out of nineillumination periods and turning all light modulators on for theremaining six periods. FIG. 9A comprises nine modulation masks MM1, MM2. . . MM9. The modulation masks have been inspired by the modulationmask of FIG. 8A in such a way that applying the mask of FIG. 8Arepeatedly for nine illumination periods equals applying each of themodulation masks MMI to MM9 once. All columns of the first modulationmask MM1 of FIG. 9A are, thus, equal to the right-most column of themask of FIG. 8A, all columns of the modulation mask MM2 are equal to thesecond right-most column of the mask of FIG. 8A and so on. Thereby, itis ensured that the uniform intensity distribution facilitated by themask of FIG. 8A is maintained while the intensity peaks are alsohandled.

FIG. 9B corresponds to FIG. 8B except for the contents of the modulationmask row that is moved over the light sensitive points. As themodulation mask in the present embodiment of the invention actuallycomprises a bank of modulation masks MM1 . . . MM9, the modulation maskrow in FIG. 9B is changed for each illumination period as indicated bythe references MM1 . . . MM9. The columns 91, 92, 93, 94 again containthe intensities experienced by each of the light sensitive points LSP1,LSP2, LSP3, LSP4. By the modulation mask adaptation technique of thepresent embodiment, it is ensured that all light sensitive pointsexperience the same amount of light at each illumination period.Thereby, it is also ensured that, in the present example, all pointsreceive three standard intensity exposures, three peak intensityexposures, and three exposures without light.

FIG. 9C comprises a diagram corresponding to that of FIG. 8C showing theenergy accumulation taking place. Contrary to the example of FIG. 8C,the light sensitive points in this example, however, absorb exactly thesame amount of energy. From this diagram, it is also evident that theblocked light modulators, i.e., the modulation mask has beensynchronized with and locked to the time and the intensity peaks insteadof the light modulation layout.

Regarding the algorithm described above, the use of masks forcompensating intensity peaks as described above with reference to apreferred embodiment of the present invention causes an additional stepto be inserted such that typically the light sensitive medium 5, e.g., aprinting plate, by means of, e.g., a DMD-based light modulationarrangement 1, is exposed to a desired image by looping through analgorithm comprising the steps of: (1A) on the basis of digitally storedinformation about the full or partial image to expose, establishing abitmap comprising settings for each of the light modulators LM for thecurrent relative position between the light modulating arrangement 1 andthe light sensitive medium 5, (1Aa) establishing, by loading and/orprocessing, a modulation mask MM, (1B) establishing a composite bitmapby combining the established bitmap with a modulation mask MM by meansof a bitwise AND-operations, (2) loading the established compositebitmap into the DMD-chip internal memory, (3) instructing the DMD-chipto engage the light modulators LM according to the loaded data, (4)after a certain time determined on the basis of, e.g., the scanningspeed, peak timing, etc., instructing the DMD-chip to disengage thelight modulators LM.

It is noted that the bank of masks illustrated in FIG. 8A is merely anexample and that any scheme or method of determining, establishing oradapting the modulation masks, whether at runtime or preceding theexposure, are within the scope of the present invention. It is,furthermore, noted that the timing of mask adaptation does notnecessarily need to correspond to the illumination periods, scanningspeed, etc., but may be determined on the basis of any parameters.

In a preferred embodiment of the invention, the modulation mask or bankof masks is optimized to never turn off light modulators at peak times.This is to actually exploit the extra energy comprised by the intensitypeaks and, thus, benefit from the otherwise annoying and problematicpeaking power supply. It is, however, noted that also modulation masksblocking some or all of the peaks are within the present invention.

A further embodiment of the present invention comprises a lightmodulating arrangement comprising a spatial light modulator and the useof modulation masks for avoiding non-uniform intensity distribution overthe light modulation layout. In order to enable the use of peaked lightsources, the modulation masks are, during scanning, shifted in adirection along or opposite the scanning direction, by an amount of oneor more light modulator widths. Thereby, the modulation mask may besynchronized with and locked to the intensity peaks.

Due to clarity, the intensity peaks have, in the above examples, been ofa width approximately corresponding to the width of one illuminationperiod, i.e., the time it takes for the light modulation layout to movefrom the edge of one light sensitive point to the edge of the nextpoint. The peaks are, however, typically not related to the otherparameters at all and any correspondence between the frequency and widthof the intensity peaks and the illumination periods, the scanning speed,etc., is within the scope of the present invention.

The further problem by using light sources with peaking power suppliesdescribed above with reference to FIG. 3B, i.e., the problem of thedifference between the intensity floor level and the intensity peaklevel changing over a considerable time, e.g., significantly over 200hours, is also addressed by the above-described embodiments of thepresent invention as such changes are insignificant as long as the peaksare either fully exploited for all light sensitive points or fullysilenced for all light sensitive points, e.g., by blocking lightmodulators at peak times.

An alternative embodiment of the present invention is primarily directedagainst light modulating arrangements exercising a stepping movementpattern instead of a scanning movement pattern. When such a movementpattern is used, each light sensitive point LSP is illuminated for acertain time by one light modulator LM which is positioned steadily overthe light sensitive point. The illumination may be repeated by the sameor a different light modulator LM, and for the same of a differentamount of time. The energy accumulation does, thus, in this alternativeembodiment, not primarily depend on the number of light modulatorsilluminating it during a scanning movement but rather of the time spanthe one light modulator is positioned (and turned on) over a specificlight sensitive point. Thereby, the use of constant modulation masks isimpossible as a blocked light modulator would cause no light at all toreach the corresponding light sensitive point.

In order to overcome this, an embodiment of the present inventioncomprises changing the modulation mask during exposure. The changes maybe applied at a certain frequency or at any possible time, and maycomprise periodic, pseudo random or random enabling and disabling oflight modulators. The change timing and matter should preferably besynchronized with the intensity peak timing. A certain embodiment ofthis may also be described as a pile of modulation masks, whereof atcertain times or according to a certain frequency, the uppermost mask isapplied, and the formerly applied mask is put in the bottom of the pile.Preferably the application of the first mask should be synchronized withthe peak timing.

A variant of this embodiment comprises applying modulation masks to theillumination time spans. By monitoring and/or controlling the intensitypeak timing and amount, it is possible to adjust the illumination times,i.e., apply a modulation mask to the times, when intensity peaks occur.

It is noted that the present invention has several further uses thandescribed above. It may, furthermore, with advantage be used, e.g., forexposing printed circuit boards in connection with the manufacture ofsuch boards, rapid prototyping and rapid manufacture, i.e., manufactureof three-dimensional models by a process well-known as rapid prototypingor rapid manufacture, exposing offset plates and films, in serigraphyapplications, in photo finishing processes, in biomedical applications,e.g., for research regarding DNA profiles, in projection applicationsand signs, in digital cinema applications, etc., and in any otherapplication or process comprising light sources and where the possibleuniformity of accumulated energy in different points at a lightsensitive media may have a certain importance.

1. A method for enabling transmission of substantially equal amounts ofenergy from at least one light source to at least two light sensitivepoints, wherein a resulting luminous intensity of the light source is asubstantially continuous wave mode and comprises intensity variations intime in the form of substantially periodic intensity peaks, comprisingthe steps of: controlling said transmission by at least one illuminationarrangement; establishing a correlation between said intensityvariations and at least one feature of said illumination arrangement;moving said at least one illumination arrangement and said at least twolight sensitive points relative to each other, wherein said at least onefeature of said illumination arrangement comprises characteristics ofsaid relative movement; and wherein said step of establishing acorrelation further comprises adapting said characteristics of saidrelative movement into synchronism with said intensity variations intime or adapting said intensity variations in time into synchronism withsaid characteristics of said relative movement, and said synchronismbetween said intensity variations and said characteristics of saidrelative movement comprise an integer number of said periodic intensitypeaks to occur during the illumination of each of said at least twolight sensitive points.
 2. The method of claim 1, wherein saidillumination arrangement comprises at least one light modulation system,and said at least one feature of said illumination arrangement comprisescharacteristics of said light modulation system.
 3. The method of claim2, wherein said at least one light modulation system comprises at leastone spatial light modulator comprising a plurality of light modulators.4. The method of claim 2, wherein said controlling of said transmissionby said at least one illumination arrangement comprises controlling saidcharacteristics of said at least one light modulation system at leastpartly on the basis of at least one modulation mask defining lightmodulators to be disabled.
 5. The method of claim 4, wherein saidestablishment of a correlation comprises adapting said at least onemodulation mask so that said characteristics of said at least one lightmodulation system is controlled in synchronism with said intensityvariations in time.
 6. The method of claim 5, wherein said adapting ofsaid at least one modulation mask is performed continuously.
 7. Themethod of claim 5, wherein said adapting of said at least one modulationmask comprises choosing a predefined modulation mask from a bank ofmodulation masks.
 8. The method of claim 4, wherein said at least onemodulation mask further comprises control information for avoidingnon-uniform energy transmission due to intensity variations in spacecaused by said light modulation system or optical features of saidillumination arrangement.
 9. The method of claim 8, wherein saidestablishment of a correlation comprises rearranging said controlinformation in time.
 10. The method of claim 8, wherein saidestablishment of a correlation comprises rearranging said controlinformation in space.
 11. An illumination arrangement for controllingtransmission of energy to at least two light sensitive points, whereinsaid controlling transmission enables transmission of substantiallyequal amounts of energy to each of said at least two light sensitivepoints; said illumination arrangement comprises at least one lightsource substantially driven in continuous wave mode; said at least onelight source is adapted to submit light comprising substantiallyperiodic intensity variations; said illumination arrangement comprisesat least one light modulation system comprising at least one spatiallight modulation system; said transmission of substantially equalamounts of energy to each of said at least two light sensitive points isat least partly enabled by controlling relative movement between saidillumination arrangement and said at least two light sensitive points;and said controlling of said relative movement comprises synchronizingsaid relative movement with said periodic intensity variations in such away that an integer number of said periodic intensity peaks occur duringthe illumination of each of said at least two light sensitive points.12. The illumination arrangement of claim 11, wherein said at least onespatial light modulation system comprises a DMD-chip.
 13. Theillumination arrangement of claim 11, wherein said at least one spatiallight modulation system comprises a micro-mechanical shutter array. 14.The illumination arrangement of claim 11, wherein said illuminationarrangement is moved relative to said at least two light sensitivepoints.
 15. The illumination arrangement of claim 11, wherein saidtransmission of substantially equal amounts of energy to each of said atleast two light sensitive points is at least partly enabled bycontrolling said light modulation system.
 16. The illuminationarrangement of claim 15, wherein said controlling said light modulationsystem comprises applying at least one modulation mask.
 17. Theillumination arrangement of claim 16, wherein said at least onemodulation mask is established on the basis of characteristics of saidperiodic intensity variations.
 18. The illumination arrangement of claim16, wherein said at least one modulation mask further comprises controlinformation for handling further disadvantages of said illuminationarrangement.
 19. The illumination arrangement of claim 18, wherein saidcontrolling of said light modulation system comprises rearranging saidcontrol information for handling further disadvantages.